GMPV9.3

GMPV9 EDI
Volcano-glacier interactions: Arctic, Antarctic, and globally 

Glaciers and volcanoes interact in a number of ways, including instances where volcanic/geothermal activity alters glacier dynamics or mass balance, via subglacial eruptions or the deposition of supraglacial tephra. Glaciers can also impact volcanism, for example by directly influencing mechanisms of individual eruptions resulting in the construction of distinct edifices. Glaciers may also influence patterns of eruptive activity when mass balance changes adjust the load on volcanic systems, the water resources and hydrothermal systems. However, because of the remoteness of many glacio-volcanic environments, these interactions remain poorly understood.
In these complex settings, hazards associated with glacier-volcano interaction can vary from lava flows to volcanic ash, lahars, landslides, pyroclastic flows or glacial outburst floods. These can happen consecutively or simultaneously and affect not only the earth, but also glaciers, rivers and the atmosphere. As accumulating, melting, ripping or drifting glaciers generate signals as well as degassing, inflating/ deflating or erupting volcanoes, the challenge is to study, understand and ultimately discriminate these potentially coexisting signals. We wish to fully include geophysical observations of current and recent events with geological observations and interpretations of deposits of past events. Glaciovolcanoes also often preserve a unique record of the glacial or non-glacial eruptive environment that is capable of significantly advancing our knowledge of how Earth's climate system evolves.
We invite contributions that deal with the mitigation of the hazards associated with ice-covered volcanoes in the Arctic, Antarctic or globally, that improve the understanding of signals generated by ice-covered volcanoes, or studies focused on volcanic impacts on glaciers and vice versa. Research on recent activity is especially welcomed. This includes geological observations e.g. of deposits in the field or remote-sensing data, together with experimental and modelling approaches. We also invite contributions from any part of the world on past activity, glaciovolcanic deposits and studies that address climate and environmental change through glaciovolcanic studies. We aim to bring together scientists from volcanology, glaciology, seismology, geodesy, hydrology, geomorphology and atmospheric science in order to enable a broad discussion and interaction.

Co-organized by CR3/GM7/NH2/SM1, co-sponsored by IACS and IAVCEI
Convener: Eva EiblECSECS | Co-conveners: Iestyn Barr, Adelina Geyer, gioachino roberti
Presentations
| Fri, 27 May, 08:30–10:00 (CEST)
 
Room -2.47/48

Presentations: Fri, 27 May | Room -2.47/48

Chairpersons: Eva Eibl, Iestyn Barr, gioachino roberti
08:30–08:33
08:33–08:40
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EGU22-10267
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ECS
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On-site presentation
Amelia Vale, Jeremy Phillips, Alison Rust, and Geoff Kilgour

Pyroclastic density current (PDC) interactions with ice are common at high altitude and latitude stratovolcanoes. When PDCs propagate over ice, melt and steam are generated. The incorporation of melt and steam into PDCs can alter the flow dynamics by reducing friction at the particle-ice interface and between individual particles. Melt incorporation can also transform a PDC into an ice-melt lahar. The hazardous and temporally unpredictable nature of these flows limits field observations. Conceptual models of PDC-ice interactions for hazard assessment and modelling exist, but quantifications of the microscale physical processes that underpin these interactions are limited. We use experiments to characterise the melting and friction reduction that occur when PDCs are emplaced onto ice.

In experiment set one, a heated particle layer was rapidly emplaced onto a horizontal ice layer contained within an insulated beaker 7.3 cm in diameter. The particle types used were glass ballotini, crushed pumice, and Ruapehu PDC samples, covering a diverse range of grain characteristics. The particle layer was varied in thickness up to 45 mm and across temperatures up to 700 °C. In each experiment, the mass of melt and steam were quantified, and the time evolution of temperature through the particle layer was measured.

Across all particle types, increasing particle layer mass (therefore layer thickness) and temperature increased melt and steam production. However, Ruapehu and pumice melt masses showed greater sensitivity than ballotini to particle temperature for any given layer thickness. Conversely, steam production was greater for the ballotini for any given layer thickness and was more sensitive to ballotini particle temperature.

Localised steam escape, fluidisation, capillary action, and particle sinking, were observed to varying extents in the experiments. These phenomena caused melt to be incorporated into the particle layer. The rate of increase in melt generation decreases with increasing particle layer thickness. This is due to increasing steam production, the increasing temperature of incorporated meltwater, energy losses to the atmosphere, and alterations to the bulk particle diffusivity.

Experiment set two characterised the mobility of particles over frozen and non-frozen substrates. Pumice and Ruapehu particles of varying temperature and layer thickness were poured into a 4.5 cm diameter alumina tube, which was rapidly lifted, allowing the particles to radially spread over the substrate. This configuration has been widely studied in experiments on granular flow mobility. The initial and final aspect ratios of the particle layer were measured, and conform to a power-law form previously interpreted as showing that frictional interactions are only important in the final stages of flow emplacement. Enhanced particle layer mobility over ice was only observed for Ruapehu particles above 400 °C, which we interpret to be due to fluidisation of the particles by rising steam. This is consistent with experiment set one, where Ruapehu particles produced more steam than pumice, and were often fluidised above 400 °C.

Experimental data will be used to calibrate surface flow hazard models for PDC runout and lahar generation, enabling prediction of PDC-ice interaction hazards. These models will be tested at Mt. Ruapehu, New Zealand. 

How to cite: Vale, A., Phillips, J., Rust, A., and Kilgour, G.: Pyroclastic Density Currents Over Ice: An Experimental Investigation of Microphysical Heat Transfer Processes , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10267, https://doi.org/10.5194/egusphere-egu22-10267, 2022.

08:40–08:47
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EGU22-10002
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ECS
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On-site presentation
Raquel Arasanz, Oriol Vilanova, Adelina Geyer, Meritxell Aulinas, Jordi Ibañez-Insa, Antonio M. Álvarez-Valero, Helena Albert, and Olga Prieto-Ballesteros

Hydrothermal systems, commonly developed in volcanic calderas, play an important role on the type and location of the post-caldera volcanic activity. The hydrothermal alteration and mineral precipitation can modify the physical properties and mechanical behaviour of the affected rocks, with the progressive alteration facilitating the occurrence of phreatic or hydrothermal explosive eruptions. Deception Island (South Shetland Islands) is one of the most active volcanoes in Antarctica, with more than 20 eruptions and three documented unrest periods over the past two centuries. The island consists of a composite volcano with an 8.5 x 10 km centrally located caldera dated at c. 8,300 years, according to paleomagnetic data, and 3,980 ± 125 calibrated years before the present (cal yr BP) based on tephrochronology, sedimentological studies and 14C dating. After the caldera-forming event, volcanic activity has been characterized by monogenetic magmatic and phreatomagmatic eruptions located around the caldera rim. Also, a hydrothermal system developed in the Port Foster area, although no detailed study has been done so far. The aim of this work is to shed further light in the dynamics of Deception Island hydrothermal system by studying several representative samples of magmatic rocks. A detailed petrographic study and a characterization of primary and secondary minerals have been carried out. The presence of secondary minerals and the palagonite alteration in the Fumarole Bay Formation suggest that the alteration of the samples took place under conditions of low water/rock ratios, basic pH and temperatures below 200 °C. The secondary minerals from the Basaltic Shield Formation samples may be indicative of fluids with temperatures higher than 200 °C and richer in CO2. Finally, the physical changes observed in the samples of this study lead to the conclusion that the investigated areas of the Fumarole Bay Formation are more likely to host hydrothermal or phreatic explosive eruptions, compared to the Basaltic Shield Formation zones.

This research is part of POLARCSIC research initiatives and was partially funded by the MINECO grants POSVOLDEC(CTM2016-79617-P)(AEI/FEDER-UE) and VOLGASDEC (PGC2018-095693-B-I00)(AEI/FEDER, UE) and the grant PID2020-114876GB-I00 funded by MCIN/AEI/ 10.13039/501100011033 and, as appropriate, by “ERDF A way of making Europe”, by the “European Union” or by the “European Union NextGenerationEU/PRTR”. This research is also supported by the PREDOCS-UB grant.

How to cite: Arasanz, R., Vilanova, O., Geyer, A., Aulinas, M., Ibañez-Insa, J., Álvarez-Valero, A. M., Albert, H., and Prieto-Ballesteros, O.: Characterization of alteration minerals in Deception Island (Antarctica): implications for the dynamics of the current hydrothermal system, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10002, https://doi.org/10.5194/egusphere-egu22-10002, 2022.

08:47–08:54
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EGU22-8774
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ECS
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Presentation form not yet defined
Katie Reeves, Jennie Gilbert, Stephen Lane, and Amber Leeson

Volcanoes can generate pyroclastic material that is deposited on ice and snow surfaces. However, a range of particle properties and spatial distribution of layer thicknesses are associated with deposition of volcanic material1. This can modify the thermodynamic behaviour and optical properties of clean ice. Typically, thin layers of particles (i.e. in ‘dirty’ ice conditions) can increase ice ablation, whilst thick layers of particles (i.e. in ‘debris-covered’ conditions) can hinder ablation2. Therefore, the state of ice is an important control on the energy balance of an ice system. 20.4% of Earth’s known Holocene volcanoes are associated with glacier or permanent snow cover3, and so it is crucial to understand how volcanic material interacts with ice systems to (1) better understand the evolution of debris-covered and dirty ice in general and (2) forecast future ice-melt scenarios at individual ice-covered volcanoes.

We present laboratory experiments that systematically reviewed the impact of volcanic particles of a range of compositions and properties (e.g. thermal conductivity, diameter, density, and albedo) on ice. Experiments assessed single particles and a scattering of particles on optically transparent and opaque ice, subjected to visible light illumination from a light emitting diode in a system analogous to dirty ice. Automated time-lapse images and in-person observations captured the response of particles and ice to radiation. Particles investigated included trachy-andesitic cemented ash particles from Eyjafjallajökull (Iceland), basaltic-andesitic scoria from Volcán Sollipulli (Chile), and rhyolitic pumice from Mount St. Helens (USA).

The experiments provided insight into some of the processes associated with volcanic particle interaction with ice. Results demonstrated that all volcanic particles with varying albedos induced ice melt and drove convection systems within the meltwater. This convection resulted in indirect heating beyond the immediate margins of the particles. The particles additionally lost finer grained fragments to meltwater, further driving ice melt through the addition of multiple absorbing surfaces within the ice system. This demonstrated that volcanic particles have the capability to melt ice very effectively in dirty ice conditions. In all experiments, the particles had a low thermal conductivity (relative to ice), although the density differed between particle types. Our experiments showed that the porosity and density of a volcanic particle can dictate the behaviour of particle-ice interaction; a dense particle can melt downwards through the ice (in similarity with the behaviour of iron-based meteorites4), whilst a less dense particle can become buoyant in meltwater, resulting in an extensive area of surface melt.

1. Möller et al. (2018), Earth Syst. Sci. Data, https://doi.org/10.5194/essd-10-53-2018

2. Fyffe et al. (2020), Earth Surf. Process. Landforms, DOI: 10.1002/esp.4879

3. Curtis and Kyle (2017), Journal of Volc. And Geo. Research http://dx.doi.org/10.1016/j.jvolgeores.2017.01.017

4. Evatt et al. (2016), Nature Comms., DOI: 10.1038/ncomms10679

How to cite: Reeves, K., Gilbert, J., Lane, S., and Leeson, A.: The role of volcanic particle thermal conductivity, density, and porosity in influencing ice melt., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8774, https://doi.org/10.5194/egusphere-egu22-8774, 2022.

08:54–09:01
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EGU22-3569
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ECS
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On-site presentation
Michael Martin, Iestyn Barr, Benjamin Edwards, Elias Symeonakis, and Matteo Spagnolo

Many (~250) volcanoes worldwide are occupied by glaciers. This can be problematic for volcano monitoring, since glacier ice potentially masks evidence of volcanic activity. However, some of the most devastating and costly volcanic eruptions of the last 100 years involved volcano-glacier interactions (e.g. Nevado del Ruiz 1985, Eyjafjallajökull 2010). Therefore, improving methods for monitoring glacier-covered volcanoes is of clear societal benefit. Optical satellite remote sensing datasets and techniques are perhaps most promising, since they frequently have a relatively high temporal and spatial resolution and are often freely available. These sources often show the effects of volcanic activity on glaciers, including ice cauldron formation, ice fracturing, and glacier terminus changes. In this study, we use satellite sources to investigate possible links between volcanic activity and changes in glacier velocity. Despite some studies reporting periods of glacier acceleration triggered by volcanic unrest, the potential of using the former to monitor the latter has yet to be investigated. Our approach is to observe how glacier surface velocity responded to past volcanic events in Alaska and Chile by applying feature-tracking, mostly using optical satellite imagery. The overall aim is to systematically track changes in the glacier velocity, with hope of improving volcano monitoring and eruption prediction. 

How to cite: Martin, M., Barr, I., Edwards, B., Symeonakis, E., and Spagnolo, M.: Volcanically-triggered changes in glacier surface velocity , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3569, https://doi.org/10.5194/egusphere-egu22-3569, 2022.

09:01–09:08
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EGU22-4743
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ECS
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Presentation form not yet defined
Joseph Graly, Siri Engen, and Jacob Yde

As loci of the fresh formation of alkaline rock, volcanic islands are hotspots of geochemical activity. Collectively volcanic islands are responsible for approximately one third of the global long term CO2 drawdown from chemical weathering. Glaciers also form environments with substantial chemical weathering activity. Despite zero-degree temperatures, subglacial environments provide both freshly ground down mineral surfaces and highly dilute meltwaters, allowing chemical processes to occur at faster rates than in warmer settings where reactions occur near chemical saturation. Yet, the degree to which glaciation enhances weathering on volcanic islands has received relatively little study.

Beerenberg, Jan Mayen, Norway, is the world´s northernmost active stratovolcano. It is mostly glacierized, with 23 distinctly named glaciers descending from the top of the volcanic cone to the sea. Many of the Beerenberg glaciers release sediment-laden subglacial water, indicative of water-rock interaction in subglacial environments. In August 2021, we did a preliminary survey of the aqueous geochemistry and sediment composition of several subglacial outlets at Beerenberg’s largest glacier, Sørbreen. We also surveyed glacial surface streams, glacial ice and snow, non-glacial melt streams, springs, and proglacial lakes.

The subglacial waters of Sørbreen are strongly enriched in bicarbonate, with little chloride despite the marine location and only trace amounts of other anions. Cation composition is ~60% Na and K and 40% Ca and Mg by mole, suggesting a balance between divalent and monovalent cations reflective of local bedrock. Together this strongly suggests carbonation weathering of silicate minerals as the source of the vast majority of dissolved load in the subglacial waters. Non-glacial waters are more dilute and enriched in sea water derived ions (Cl, SO4, and Na) compared to subglacial waters.  

While a complete geochemical budget is not possible from our initial observations, these results imply that Beerenberg is a hot spot of chemical weathering. If our dissolved CO2 fluxes are representative of long-term averages, then atmospheric CO2 drawdown at Sørbreen is comparable to other glacierized mafic volcanic rock regions, such as those on Iceland and Disko Island. These atmospheric CO2 drawdown rates are approximately double the world average and a factor of five higher than the drawdown in non-glacierized high latitude regions.

How to cite: Graly, J., Engen, S., and Yde, J.: Preliminary Geochemical Assessment of the Subglacial Environment of Beerenberg, the World’s Northernmost Active Stratovolcano, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4743, https://doi.org/10.5194/egusphere-egu22-4743, 2022.

09:08–09:15
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EGU22-8641
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ECS
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On-site presentation
Anna Margrét Sigurbergsdóttir and Magnús Tumi Gudmundsson

Tuyas are basaltic to intermediate glaciovolcanic edifices, formed in a body of meltwater within an ice sheet, in an ocean or a lake. The most common tuya stratigraphy consist of a lowermost layer or a mound of pillow lava, overlain by hyaloclastite tuffs and capped by a layer of subaerially-formed, horizontally bedded, lava flows. The parts of the lava flows more distant from the vent are built on flow-foot breccias, with the transition from subaerially-formed lava flows and breccias being a distinct stratigraphic boundary: the passage zone. The elevation of the passage zone marks the water level in the englacial lake into which the evolving tuya was built. At many locations the elevation of the passage zone appears to vary considerably from one location on a tuya to another. Some tuyas are elongated. One idea is that the elongation is predominantly in the direction of ice flow at the time of eruption.

By studying tuyas through aerial photography, satellite imagery and ground observations, the edifices variations in the elevation of the passage zone can be studied. This provides information on the eruption processes and environmental conditions at the time of formation.  We have analyzed the variation of passage zone elevation with distance along strike of a selected set of tuyas in Iceland. These include Bláfjall, located in Northern Iceland. It was formed within a Pleistocene ice sheet a continuous, prolonged eruption, or in a series of eruptions, closely spaced in time. The lava cap reaches a maximum thickness of approximately 100 m but is only a few meters to a few tens of meters thick on average, showing clear signs of influence from the ice sheet. Apparently, both the thickness of the ice sheet and the direction of ice flow direction exerted major control on the height and elongation of the Bláfjall tuya. The eruption took place well to the north of the ice divide at the time, and the flow of ice was predominantly from south to north, with the elongated structure of the tuya oriented parallel to the flow of the ancient glacier. The thickness of the lava cap is greatest in the north part and generally decreases towards south. This is despite the fact that the elevation of the mountain increases southwards. This indicates that the northern part is mostly formed by an advancing lava delta, propagating in the direction of ice flow and that the level of the water body present at the end of the advancing lava delta become progressively lower towards north. This suggests a sloping ice sheet at the time of formation, or possibly a receding ice sheet, leading to gradual thinning with time as the eruption progressed.   

How to cite: Sigurbergsdóttir, A. M. and Gudmundsson, M. T.: The Bláfjall tuya in North Iceland, morphological characteristics and effect of ice flow and icesheet slope on edifice form  , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8641, https://doi.org/10.5194/egusphere-egu22-8641, 2022.

09:15–09:22
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EGU22-8667
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ECS
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On-site presentation
Irma Gná Jóngeirsdóttir, Magnús Tumi Gudmundsson, and Gudrún Larsen

Gjálp is a hyaloclastite ridge situated beneath the western part of the ~8000 km2 Vatnajökull ice cap, located midway between the subglacial calderas of Grímsvötn and Bárdabunga volcanoes. The tephra erupted at Gjálp has affinities fitting with the Grímsvötn volcanic system while the associated seismicity and unrest preceding the eruption suggest that the eruption was caused by lateral magma flow from Bárdarbunga.  Eruptions occurred at Gjálp in 1938 and 1996 but only the 1996 eruption is thought to have broken through the ice. The 1996 eruption was first detected on the 30th of September at about 22:00 GMT by the onset of seismic tremor; the following day heavily crevassed ice cauldrons were noticed. Around 30 hours after detection of the tremor the eruption broke through the ice sheet. The eruption lasted for 13 days, during which a 6-7 km long subglacial, hyaloclastite ridge was formed. The subglacial eruption melted large volumes of ice that accumulated within the Grímsvötn caldera until early November, when it was released in a major jökulhlaup, destroying bridges and damaging roads. In comparison with the subglacial eruption the subaerial part was relatively modest. The style of activity was mostly Surtseyan and the tephra erupted is mildly intermediate in composition.

The tephra fall began on October 2 and continued intermittently until October 13. The first tephra was seen at 05:18 on October 2. By 08:50 the largest explosions threw tephra about 1 km above the ice surface and the plume rose to 4-4.5 km above sea level. This tephra was carried north and north-northeast across North and Central Iceland and was detected as far as 250 km from source. On October 3 the plume was reported to have reached 8-9 km a.s.l. Tephra was also dispersed to the east and south and most of the tephra accumulated on the Vatnajökull glacier. During the eruption, repeated snow fall caused layering within the tephra deposit. In the following year samples were collected from the tephra fall area on the glacier. These consist mostly of snow cores with tephra thickness ranging from dm to mm. The samples were processed to estimate the tephra volume and to create a dispersal and isopach map. The tephra layer deposited on the glacier is volumetrically only a few percent of the bulk volume (~0.7 km3) of the subglacial ridge formed in the 1996 eruption.

How to cite: Jóngeirsdóttir, I. G., Gudmundsson, M. T., and Larsen, G.: Tephra layer formed in the 1996 eruption of Gjálp, Iceland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8667, https://doi.org/10.5194/egusphere-egu22-8667, 2022.

09:22–09:32
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EGU22-8751
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ECS
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solicited
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Highlight
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Presentation form not yet defined
Hannah Iona Reynolds, Magnús T. Gudmundsson, and Thórdís Högnadóttir

Jökulhlaups (glacier outburst floods) are considered the most common type of volcanic hazard in Iceland, and result from the accumulation of meltwater during long-term geothermal activity beneath glaciers, or very rapid melting over a short period of time. Jökulhlaups may occur without visible precursors or prior warning, varying in size from being persistent leakage to floods that have caused considerable damage like the jökulhlaups in Múlakvísl and Kaldakvísl in July 2011. Little has been known about the onset time of water accumulation/melting, whether water accumulated before it was released, and how these events are related to intrusion of magma. This study categorises known ice cauldrons within Icelandic glaciers based on their volume, rate of formation, and longevity. Geothermal reservoir modelling was then used to explore possible heat sources which generate the cauldrons. Five scenarios were simulated: (1) Subglacial eruption – freshly erupted magma in direct contact with the ice at the glacier base; (2) Intrusion into homogeneous bedrock - magma intrudes into a bedrock of homogeneous properties; (3) Intrusion into high permeability channel – similar to scenario (2) but a high permeability channel extends from the intrusion to the glacier-bedrock boundary, e.g. zone of high permeability at a caldera fault; (4) Sudden release of pressure – a hot reservoir is topped by caprock, with a high permeability pathway from depth up to the glacier-bedrock boundary, representing a sudden breach of a pressurised reservoir; and (5) Intrusion into a very hot reservoir – similar to scenario (3) but the reservoir is near boiling point, from previous repeated intrusive activity. This work improves our understanding of sudden and unexpected jökulhlaups, which is helpful for hazard assessments and response plans for unrest in glaciers near inhabited areas, tourist spots, and power plants. 

How to cite: Reynolds, H. I., Gudmundsson, M. T., and Högnadóttir, T.: The causes of unexpected jökulhlaups, studied using geothermal reservoir modelling , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8751, https://doi.org/10.5194/egusphere-egu22-8751, 2022.

09:32–09:39
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EGU22-6528
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ECS
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Virtual presentation
Rosie Cole, Magnús Gudmundsson, Birgir Óskarsson, Catherine Gallagher, Guðrun Larsen, and James White

The Katla volcanic system is one of the most productive in Iceland. Frequent basaltic and occasional silicic phreatomagmatic eruptions through the ice cap Mýrdalsjökull have provided a rich Holocene tephra record. Understanding of pre-Holocene eruptions and the thickness and extent of ice cover during glacial periods is much more limited.

We present eruption and emplacement models for three formations exposed on the flanks of the Katla volcano. Two are rhyolitic nunataks and one is an alkali basaltic sequence. These formations rise above the surrounding ice and topography, respectively, and show evidence for ice-confined emplacement, indicating their formation at a time when ice cover was thicker and more extensive.

Our models of each formation are based on field study, a photogrammetry survey, and major element geochemical analyses. The basaltic formation of Morinsheiði is an intercalated sequence of volcaniclastic rocks, pillow lavas and pillow breccias, entablature-jointed and lobate lavas, and more massive pahoehoe lava sheets, intruded by several dykes. The top of the sequence is a glacially eroded surface and it is bounded on all sides by deep valleys. The Enta nunatak is a kinked ridge or possibly two en-echelon ridges. A silicic volcaniclastic unit is intercalated with and intruded by fluidal and heavily jointed rhyolite lobes, spines and sheets. This formation is capped by a segment of crater wall composed of scoria. The Kötlujökull nunatak is tabular in shape, has a clastic base and is capped by jointed lava with lobate margins and breakout lobes descending the steep slopes.

Each formation exhibits evidence of multiple eruption styles in varying hydrological conditions, and at least for Morinsheiði a fluctuating water level. These are the preliminary results from the project “SURGE: Uncapping subglacial eruption dynamics and glacier response”, which aims to better understand the relative influences of magma chemistry, eruption style and glacial conditions on meltwater production and retention, glacial response, and the feedback effects for continued eruptions. These models, combined with new 40Ar-39Ar dating of the lavas, will also provide greater insight into the form of Katla and the glacial conditions that prevailed during the late Pleistocene.

How to cite: Cole, R., Gudmundsson, M., Óskarsson, B., Gallagher, C., Larsen, G., and White, J.: Pre-Holocene glaciovolcanism in the Katla area, south Iceland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6528, https://doi.org/10.5194/egusphere-egu22-6528, 2022.

09:39–09:46
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EGU22-12210
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Presentation form not yet defined
Catherine (Kate) Gallagher, Magnús Tumi Gudmundsson, Thorvaldur Thordarson, Bruce Houghton, Birgir Óskarsson, Robert Askew, Rosie Cole, William Moreland, Valentin Troll, and Guðrún Þorgerður Larsen

Iceland has the largest variety of subglacially formed volcanic edifices worldwide, given the extensive glacial cover during the Pleistocene and its frequent volcanic activity. As substantial parts of the volcanic zones are presently ice-covered, eruptions beneath glaciers are common.

 

Phreatomagmatic activity and flood deposits have been hypothesised for shallow subglacial fissure eruptions, at or within a glacial margin. However, to date, no historical examples that did not immediately break through the ice, resulting in dry magmatic activity, have been directly observed. Also, at dynamic ice-margin settings, no extensive resultant formations from shallow subglacial fissure eruptions formed in older historic eruptions have been studied until now. 

 

The final fissure from the 1783–84 CE Laki basaltic flood lava event in the Síða highlands of Iceland, fissure 10, provides a perfect natural laboratory to understand the eruptive dynamics of a shallow subglacial or intraglacial fissure eruption. Fissure 10 is a 2.5 km long formation, which constitutes the final phase of activity on the 29 km long Laki crater row, formed as eruptive activity from the Laki eruption propagated under Síðujökull, an outlet glacier from the Vatnajökull ice-cap. The resultant eruptive sequences display evidence of the increasing influence of ice when traced along strike from SW to NE, with the eruption transitioning to a predominantly phreatomagmatic phase with increasing degrees of lateral confinement. The sequence is dominated by volcanoclastic units, formed by multiple phreatomagmatic and magmatic phases suggestive of fluctuating water levels, intercalated with hackly jointed intrusions, hackly jointed lobate lava flows and debris flows. Repeating units of agglutinated spatter and spatter-fed lava flows cap the sequence, suggesting decreasing influence of external water with stratigraphic height and towards the end of the fissure’s eruptive activity. A thin layer of glacial till coats the top of the fissure 10 sequences. The margin of Síðujökull has since fully receded from the formation.

 

Our model for the eruptive dynamics of the northern Laki fissure 10 formation is based on field mapping, a drone photogrammetry survey, petrological observations and EMP analysis of glassy tephra and lava selvages to gain a full understanding of the activity and how eruptive activity progressed. The Laki eruption benefits from a wealth of previous studies on the magmatic phases from the other 9 subaerially eruptive fissures, to the SW of fissure 10, allowing for the effects of the glacier on this fissure’s activity to be isolated and defined.

 

Fissure 10 allows for an approximate reconstruction of the ice margin and glacier slope at the time of eruption, adding valuable information on the extent of the glaciers in SW-Vatnajökull in the late 18th century, and during the Little Ice Age. These shallow subglacially erupted deposits are the only fully accessible intraglacial eruptive vents, from a known historical eruption, on Earth. Detailed mapping and petrological analysis of deposits like these is important for interpreting landforms in paleo-ice margins, where transitional activity occurs.

How to cite: Gallagher, C. (., Gudmundsson, M. T., Thordarson, T., Houghton, B., Óskarsson, B., Askew, R., Cole, R., Moreland, W., Troll, V., and Larsen, G. Þ.: Characterising ice-magma interactions during a shallow subglacial fissure eruption: northern Laki, Iceland, a case study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12210, https://doi.org/10.5194/egusphere-egu22-12210, 2022.

09:46–09:53
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EGU22-12717
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Presentation form not yet defined
Magnus Tumi Gudmundsson, Thórdís Högnadóttir, Eyjólfur Magnússon, Hannah I Reynolds, Guðrún Larsen, and Finnur Pálsson

Eruptions where glacier ice has a significant effect on the style of activity occur in some parts of the world, notably the Andes, Alaska, parts of Antarctica and Iceland.  Due to its northerly latitude and considerable ice cover within the volcanically active zones, about 50% of all eruptions in Iceland occur within glaciers, which is about 15 such eruptions per century.  In the last 25 years, six such confirmed eruptions have taken place while only one minor confirmed eruption occurred in the period 1938-1996.  This is due to the episodic nature of activity in the volcanoes covered by the 7900 km2 Vatnajökull ice cap, with a new period of high activity starting with the Gjálp eruption of 1996.   Contemporary observations have therefore provided considerable empirical data on these events.  These data include glacier thickness prior to eruptions, ice cauldron development, glacier flow perturbations, melting rates and transitions from fully subglacial to explosive/partly subaerial eruptions.  In addition, some data exist that constrains the volcano-ice interaction in the eruptions of Katla in 1918, Grímsvötn in 1934 and 1983, Gjálp in 1938 and Hekla in 1947.  The majority of these events were basaltic.  However, at least two eruptions that had an initial fully subglacial phase (Gjálp 1996, Eyjafjallajökull 2010) were of intermediate composition.  The volume of subglacially-erupted magma ranged from a few million m3 to 0.45 km3 (DRE), initial ice thicknesses ranging from 50 to 750 m, and melted ice volumes between 0.01 km3 to 4 km3.  Combined, the data from the eruptions of the last 100+ years, provides important constraints on heat transfer rates, the rate of penetration of eruptions through ice, glacier response to eruption, and the potential for generation of jökulhlaups and lahars.  Post-eruption observations in Grímsvötn have revealed that craters formed in eruptions that break through the glacial cover can be partly built on ice.  These tend to be highly transient features due subsequent melting and ice movement.  Surface melting of ice by pyroclastic density currents has occurred in Iceland, but this type of activity has in the recent past mostly been confined to the occasional sub-Plinian to Plinian eruptions in e.g. Hekla volcano.   However, there are indications that such activity has played an important role in some relatively rare large Plinian eruptions at ice covered volcanoes in Iceland, as observed in e.g. Alaska and the Andes.

How to cite: Gudmundsson, M. T., Högnadóttir, T., Magnússon, E., Reynolds, H. I., Larsen, G., and Pálsson, F.: Volcano-ice interaction:  The empirical constraints derived from eruptions in Iceland in the period 1918-2015, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12717, https://doi.org/10.5194/egusphere-egu22-12717, 2022.

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